Packaging Plastic ESD requirements


I have a question about the ESD plastic being used in our facility. One of our suppliers have a dissipative type of ESD material and the values of ESD test show a very high value above 10^11. Other trays were way below limit and this kind of created a discussion internally if the trays are even ESD compliant or not.

What is the best way to test these kind of trays?
I used the simple resistance meter with clips and checked the ESD values. Is that the correct way?
What type of devices are best suited for testing esd in applications like these.